1. Field of the Invention
The present invention relates to a field emission display, more particularly, to a field emission display with improved light utilization efficiency.
2. Description of Related Art
In recent years, display devices have played an increasingly important role in daily life. For example, computers, the Internet, televisions, cell phones, personal digital assistants (PDAs) and digital cameras, all have to exchange messages through the control of a display. As compared to conventional cathode ray tube (CRT) displays, new-generation flat panel displays have the light, small and ergonomic features, but they still have the disadvantages of poor viewing angle, low brightness and high power consumption.
Among the technologies of developing flat panel display, field emission displays (FEDs) have the same feature of high image quality as the CRT displays, and the disadvantages found in liquid crystal displays (LCDs), such as poor viewing angle, small range of operating temperature and long response time, can be avoided. Generally, an FED can provide the features of high yield, short response time, great communication for display, thinner and lighter structure, wide angle of view, large range of operating temperature, and good recognition of slanting direction.
FIG. 1 is a schematic view for illustrating the work principle of a field emission display. A field emission display mainly includes a cathode electrode 12, an electron emissive layer 14, an anode electrode 15, a phosphor layer 16 and a gate electrode 19. Herein, the anode electrode 15 and the phosphor layer 16 are formed on the front substrate 17, while the cathode electrode 12; the electron emissive layer 14 and the gate electrode 19 are disposed on the base substrate 11. Accordingly, an electric field is formed between the cathode electrode 12 and the gate electrode 19 when a voltage is applied in-between, and thus the tunnel effect occurs whereby electrons are released from the electron emissive layer 14. Then, a voltage applied on the anode electrode 15 would accelerate the impact of the released electrons to the phosphor layer 16, resulting in the emission of light from the phosphor layer 16. Moreover, the gate electrode 19 can be used to accurately control the time to emit electrons and to increase the electron current density, and the gate electrode 19 and the cathode electrode 12 can be electrically separated from each other by the insulating layer 13.
In general, electrons released from the electron emissive layer 14 merely impact to the surface 161 of the phosphor layer 16, and thus the highest luminous efficiency would be found from the surface 161 of the phosphor layer 16. That is, most of light emitted from the phosphor layer 16 is limited within the device and thus cannot be transmitted outwards. In addition, since the output window of the conventional field emission display is located against the surface 161 of the phosphor layer 16, the light transmitted outward from the surface 161 of the phosphor layer 16 has to pass through the phosphor layer 16, the anode electrode 15, and the front substrate 17, which results in the reduction of light extraction efficiency. Thereby, the aforementioned conventional field emission display generally has the disadvantage of low luminous efficiency.